Bone anchoring device

ABSTRACT

A polyaxial bone anchoring device includes a bone anchoring element having a head and a shaft, a receiving part having a head receiving portion, a rod receiving portion, and a bore having a bore axis, and a pressure member movable in the bore and having a first surface for engaging the head, wherein the pressure member is movable to a first position where friction between the first surface and the head generates a preload on the head to maintain the shaft at a temporary angular position relative to the receiving part, and wherein the pressure member is configured to engage the receiving part to generate a holding force for holding the pressure member at the first position without a positive lock, and wherein the pressure member is movable in and out of the first position by applying an axial force on the pressure member greater than the holding force.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/592,309, filed Jan. 30, 2012, the contents ofwhich are hereby incorporated by reference in their entirety, and claimspriority to European Patent Application EP 12 153 154.5, filed Jan. 30,2012 the contents of which are hereby incorporated by reference in theirentirety.

BACKGROUND

1. Field of Invention

The invention relates to a bone anchoring device including a boneanchoring element having a head and a shaft for anchoring in a bone, areceiving part for coupling the bone anchoring element to a rod, and apressure member having a first surface for engaging the head and asecond surface on which the rod acts. The receiving part includes anaccommodation space for accommodating the head and a bore being incommunication with the accommodation space, the bore having a bore axis,The pressure member is configured to assume a first position in which itexerts a preload onto the head that results from friction between thefirst surface and the head to enable the shaft to be maintained in adesired angular position before locking the head in the receiving part,and a second position in which the head is locked with respect to thereceiving part. The first position may be achieved by moving thepressure member with a predefined force acting onto the pressure memberin an axial direction, and the pressure member may be maintained or heldat the first position by interaction with the receiving part, and can bereleased from the first position through action of another axial force.

2. Description of Related Art

US 2007/0118123 A1 describes a polyaxial bone anchor with increasedangulation. The polyaxial bone anchor has a locking element shaped andconfigured to allow an anchoring member, e.g. a screw or hook, topolyaxially rotate at large angles about a central axis of the boneanchor before compression locking the anchoring member within an anchorhead.

U.S. Pat. No. 7,604,656 B2 describes an apparatus including a fastener,a housing having a passage, and a spacer received in the passage andengageable with the fastener, wherein pin members retain the spacer andthe fastener in the housing and wherein an end portion of the pinmembers has a tapered surface by which the spacer is urged axiallytoward the fastener when the pin member is inserted through the housing.The pin members also apply an axial force to the spacer to preventrelative movement between the spacer and the housing when the rod isdisengaged from the spacer and the spacer engages the fastener. The pinmembers hold the spacer in frictional engagement with the fastener.

SUMMARY

Although the polyaxial bone anchoring devices described above providefor an enlarged angulation in a desired orientation, there is still aneed for an improved polyaxial bone anchoring device in terms ofsimplicity of design and handling of the device.

It is an object of embodiments of the invention to provide an improvedpolyaxial bone anchoring device.

With a polyaxial bone anchoring device according to embodiments of theinvention, a temporary clamping of a head of a bone anchoring element,with a more exact predetermined force in a desired angular position withrespect to a receiving part, without finally locking the head, can beachieved. In this condition, a pressure member exerts a preload forceonto the head in which the head is not locked, but is prevented orrestricted from freely pivoting by friction. The preload is achieved byapplying an axial force on the pressure member. The preload is thenmaintained by a radial force which acts on the pressure member, andfrictionally holds the pressure member in position with respect to thereceiving part. When the head is temporarily clamped, the alignment ofthe receiving part with respect to a rod and the insertion of the rod,is more readily facilitated, in particular, in situations in which amultitude of bone anchors are to be connected to the rod.

A mechanism to frictionally maintain the position of the head beforelocking is free from any spring members or similar parts or portions.The polyaxial bone anchoring device has few parts, and is of a simpledesign. According to an embodiment, for achieving the preload onto thehead, no further parts are required due to an interference fitconnection. Referring to the interference fit connection, radial forces,for example, arranged at a 90° angle to a longitudinal axis of thereceiving part, result from elastic deformation of the material of thepart or parts. The bone anchoring device can be manufactured easily andcost-effectively. Furthermore, existing receiving parts can be usedwithout having to redesign their shape. Only the pressure members haveto be adapted or modified, so that an interference fit between an outerdiameter of the pressure member and an inner diameter of the receivingpart can be achieved.

An amount of preload exerted onto the head by the pressure member can beexactly predefined in a simple manner during assembly by adjusting theexternally applied axial force. The preload onto the head generated inthis way is reproducible. The polyaxial bone anchoring device accordingto embodiments of the invention can be provided to the surgeon in apre-assembled manner, in which the pressure member is axially androtationally fixed by friction in the receiving part to such an extentthat it can not fall out or be rotated out of its aligned position. Thisallows for safer handling by the surgeon. Furthermore, by mounting thepressure member by means of a tool with a predetermined force, arepeatable friction. fit, or interference fit connection can beachieved.

According to a further aspect of embodiments of the present invention,the polyaxial bone anchoring device provides for an enlarged pivotangulation of the bone screw by attaching a sleeve-like insert whileequally providing high efficiency of fixation. A pivot angle of the boneanchoring element relative to the receiving part may be equal to orgreater than 45° measured from a straight position. This renders thebone anchoring device particularly suitable for, for example,applications of lateral mass fixation, for example, in the cervicalspine. The locking mechanism for locking the bone anchoring element andthe sleeve-like insert piece provides for a high clamping force on asmall surface. Therefore, the locking mechanism may be more efficient.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows a perspective exploded view of a polyaxial bone anchoringdevice with a spinal rod according to a first embodiment;

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state;

FIG. 3 a shows a cross-sectional front view of the bone anchoring deviceof FIGS. 1 and 2 in the assembled state without the rod and without afixation screw;

FIG. 3 b shows an enlarged portion of the cross-sectional front view ofthe bone anchoring device of FIG. 3 a;

FIG. 4 a shows a cross-sectional front view e., rotated from FIG. 4 a by90°) of a receiving part according to a first embodiment;

FIG. 4 b shows a cross-sectional side view of the receiving partaccording to the first embodiment;

FIG. 4 c shows a top view of the receiving part according to the firstembodiment;

FIG. 4 d shows a perspective top view of the receiving part according tothe first embodiment;

FIG. 4 e shows a perspective bottom view of the receiving part accordingto the first embodiment;

FIG. 5 a shows a cross-sectional front view of a pressure memberaccording to a first embodiment;

FIG. 5 b shows a side view of the pressure member according to the firstembodiment;

FIG. 5 c shows a top view of the pressure member according to the firstembodiment;

FIG. 5 d shows a perspective bottom view of the pressure memberaccording to the first embodiment;

FIG. 5 e shows a perspective top view of he pressure member according tothe first embodiment;

FIG. 6 a shows a cross-sectional front view of a sleeve-like insert;

FIG. 6 b shows a perspective top view of the sleeve-like insert;

FIG. 6 c shows a top view of the sleeve-like insert;

FIG. 6 d shows a perspective bottom view of the sleeve-like insert;

FIGS. 7 a to 7 h show steps of assembling the sleeve-like insert, thereceiving part, the bone anchoring element and the pressure member,according to one embodiment;

FIG. 8 a shows a cross-sectional view of a bone anchoring device in anassembled state, without a rod or a fixation screw, according to asecond embodiment, the cross-section taken perpendicular to an axis of arod channel of the device;

FIG. 8 b shows an enlarged portion of the cross-sectional view of thebone anchoring device of to FIG. 8 a;

FIG. 9 shows a perspective view of a receiving part according to asecond embodiment;

FIG. 10 shows a perspective view of a pressure member according to asecond embodiment;

FIG. 11 a shows a cross-sectional view of a bone anchoring device in anassembled state, without a rod or a fixation screw, according to a thirdembodiment, the cross-section taken perpendicular to an axis of a rodchannel of the device;

FIG. 11 b shows an enlarged portion of the cross-sectional view of thebone anchoring device of FIG. 11 a;

FIG. 12 shows a perspective view of a receiving part according to athird embodiment;

FIG. 13 shows a perspective view of a pressure member according to athird embodiment;

FIG. 14 shows a cross-sectional view of a bone anchoring device in anassembled state, without a rod or a fixation screw, according to afourth embodiment, the cross-section taken perpendicular to an axis of arod channel of the device; and

FIG. 15 shows a cross-sectional view of a bone anchoring device in anassembled state, without a rod or a fixation screw according to a fifthembodiment, the cross-section taken perpendicular to an axis of a rodchannel of the device.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 3 b, a polyaxial bone anchoring device accordingto a first embodiment includes a bone anchoring element 1 in the form ofa bone screw having a threaded shaft 2 and a head 3. The head 3typically has a spherically-shaped outer surface portion 3 a and arecess 3 b at its free end for engagement with a tool, e.g., a driver.The head 3 can be held in a receiving part 4 that couples the boneanchoring element 1 to a stabilization rod 100. In an assembled state,in the receiving part 4, a sleeve-like insert piece 5 providing a seatfor the head 3 of the bone anchoring element 1 and a pressure member 6for exerting pressure onto the head 3 can be arranged. Furthermore, afixation element in the form of a fixation screw 7 is provided forsecuring and fixing the rod 100 in the receiving part 4. In someembodiments, a bone anchoring device without the sleeve-like insertpiece 5 is also possible. In those cases, the seat for the head 3 may beprovided in the receiving part directly.

As can be seen from FIGS. 1 to 4 e the receiving part 4 has a top end 4a and a bottom end 4 b, a central axis C, and a coaxial bore 41extending from the top end 4 a in the direction of the bottom end 4 b.Adjacent to the top end 4 a, a U-shaped recess 42 is provided that formsa channel for receiving the rod 100. By means of the U-shaped recess 42,two free legs are formed, which are provided with an internal thread 43for cooperating with an outer thread of the fixation screw 7 in anassembled state (see, e.g., FIG. 2).

The coaxial bore 41 opens into an accommodation space 8 provided in alower region of the receiving part 4. The accommodation space 8 has alower opening 45 at the bottom end 4 b of the receiving part 4. Theaccommodation space 8 further includes a seat portion 46 near the bottomend 4 b of the receiving part 4, in which the sleeve-like insert piece 5can be seated. The seat portion 46 has a spherical shape in order toprovide a socket portion for a ball and socket joint formed between thesleeve-insert piece 5 and the receiving part 4. It should be noted thatthe seat portion 46 can alternatively be tapered or can have anothershape that can be used to realize a ball and socket joint. A smallestinner diameter at the lower opening 45 is smaller than a largest innerdiameter of the accommodation space 8. It shall be noted that an innerdiameter of the coaxial bore 41 does not need to be constant between thetop end 4 a and the accommodation space 8. The bore 41 may havedifferent portions with different diameters.

In order to allow the sleeve-like insert piece 5 to be introduced fromthe top end 4 a, two opposed recesses 47 a, 47 b (see, e.g., FIGS. 4 c-4e) are provided in the inner wall of the coaxial bore 41 and/or theaccommodation space 8. The recesses 47 a, 47 b may be aligned with theU-shaped recess 42. They may extend from the bottom of the U-shapedrecess 42 into the accommodation space 8. The size of the recesses 47 a,47 b is such that the sleeve-like insert piece 5 can be introduced fromthe top end in a 90° tilted or vertical position, where a width of therecesses 47 a, 47 b is greater than a height of the sleeve-like insertpiece 5 in its axial direction. The recesses 47 a, 47 b extend into theaccommodation space 8 to such an extent that inserting of thesleeve-like insert piece 5 into the seat 46 in such a tilted position isfacilitated.

The pressure member 6 is shown in particular in FIGS. 5 a to 5 e. Thepressure member 6 is substantially cylindrical, with an outer diameterthat allows the pressure member 6 to be moved within the coaxial bore 41and the accommodation space 8, for example, by means of a tool. However,in some embodiments an outer diameter of the pressure member 6 isslightly larger than an inner diameter of the coaxial bore 41 to achievean interference fit or press fit connection between the inner surface ofthe coaxial bore 41 and an outer surface 65 of the pressure member 6. Itis also possible that in some embodiments, only parts of the mentionedsurfaces form the interference fit. The pressure member 6 has an upperend 6 a and a lower end 6 b. Adjacent its lower end 6 b, the pressuremember 6 has a recess 61 with a spherical shape that matches the shapeof the outer spherical surface portion 3 a of the head 3. At the upperend 6 a, the pressure member 6 has a cylindrical recess 63 for receivingthe rod 100 therein. Furthermore, the pressure member 6 has a coaxialbore 64 for allowing access to the screw head 3 with a tool when thedevice is in an assembled state. By the coaxial bore 64 and thecylindrical recess 63, two legs are formed facing the top end 4 a. Thecoaxial bore 64 is also configured to allow a portion of the head 3 toextend therethrough when the bone anchoring element 1 is in a pivotedcondition.

The sleeve-like insert piece 5 is shown in particular in FIGS. 6 a-6 d.The sleeve-like insert piece 5 has an upper end 5 a and a lower end 5 b.Between the upper end 5 a and the lower end 5 b, the sleeve-like insertpiece 5 has a spherical-shaped outer surface portion 51. A largest outerdiameter of the sleeve-like insert piece 5 is greater than the smallestinner diameter of the lower opening 45 of the receiving part 4. Hence,the sleeve-like insert piece 5 cannot escape through the lower opening45 when it is seated in the receiving part 4. The dimension of the outerspherical surface portion 51 corresponds to the spherical-shaped seatportion 46 of the receiving part 4 in such a way that the sleeve-likeinsert piece 5 can pivot and rotate in the receiving part 4 when it isseated in the seat portion 46, When the sleeve-like insert piece 5 restsin the seat portion 46 such that its central axis 5 c is coaxial with acentral axis C of the receiving part 4, the lower end 5 b may projectout of the lower opening 45. When the sleeve-like insert piece 5 ispivoted in the receiving part 4, at least a portion of the lower end 5 bprojects out of the lower opening 45.

The sleeve-like insert piece 5 is hollow and has a central inner portion52 that is spherically-shaped with a radius corresponding to a radius ofthe spherically-shaped outer surface portion 3 a of the head 3 of thebone anchoring element 1. A lower end of the central portion 52 forms ashoulder 53. The inner diameter of the shoulder 53 is smaller than alargest outer diameter of the spherical head 3 so that the head 3 canrotate and pivot in the central spherical portion 52 of the sleeve-likeinsert piece 5, similar to a ball and socket joint. Between the shoulder53 and the lower end 5 b, a tapered portion 54 is provided that tapersoutwards to allow angulation of the bone anchoring element 1 until theshaft 2 comes into contact with the tapered portion 54 of the lower end5 b. Between the spherical central portion 52 and the upper end 5 a, atapered portion 55 is provided, which tapers outwards, An inner diameterof the tapered portion 55 and of the transition between the taperedportion 55 and the spherical central portion 52 is greater than thelargest outer diameter of the head 3, so that the head 3 can be insertedfrom the upper end 5 a into the sleeve-like insert piece 5, At the upperend 5 a, a chamfered portion 56 may be provided that may serve as a stopfor the pressure member 6.

Respective center points of the spherical central portion 52 and of theouter spherical portion 51 may be offset in such a way that the centerpoint of the inner central spherical portion 52 is shifted in adirection towards the bottom end 4 b (i.e., closer to lower end 5 b thanthe center point of the outer spherical portion 51). By means of this, arange of angulation for the bone anchoring element 1 can be furtherincreased. A height of the sleeve-like insert piece 5 in an axialdirection is less than a height of the head 3 in an axial direction,such that when the head 3 is inserted into the sleeve-like insert piece5, a portion of the spherical outer surface 3 a of the head 3 projectsfrom the upper end 5 a of the sleeve-like insert piece 5, for example,as can be seen from FIG. 3 a.

The sleeve-like insert piece 5 and the anchoring element I areindependently pivotable when the shaft 2 of the anchoring element 1 andthe lower end 5 b of the sleeve-like insert piece 5 are out of contact.When the shaft 2 of the bone anchoring element 1 is pivoted and engagesthe lower end 5 b of the sleeve-like insert piece 5, further pivoting ofthe bone anchoring element 1 in a direction corresponding to the contactcauses the sleeve-like insert piece 5 to pivot together with the boneanchoring element 1. When the pressure member 6 is in contact with thehead 3, there may be a gap between the pressure member 6 and thesleeve-like insert piece 5.

As indicated by arrows in FIGS. 3 a, 3 b, a force F which is providedfrom above in the figures is divided between frictional resistance(indicated by the two horizontal arrows in FIG. 3 a) and a preload force(indicated by the small arrows in FIG. 3 b), which holds the head withrespect to the receiving part 4 in a desired angular orientation byfriction. The frictional resistance results from the interference fitconnection between the pressure member 6 and the receiving part 4, wherethe outer diameter of at least one portion of the pressure member 6 isslightly larger than the inner diameter of a corresponding portion ofthe receiving part 4. The preload force acting on the head 4 leads to asmall elastic preload of the whole system.

The steps of pre-assembling the bone anchoring device according to thefirst embodiment are shown with respect to FIGS. 7 a to 7 h. The boneanchoring device according to the first embodiment may be pre-assembledin such a way that, first the sleeve-like insert piece 5 is tilted by90° and inserted into the receiving part 4 at the position of theU-shaped recess 42, as can be seen in FIGS. 7 a and 7 b. As shown inFIG. 7 b the sleeve-like insert piece 5 is moved downwards into theaccommodation space 8. Since the largest outer diameter of thesleeve-like insert piece 5 is larger than the smallest inner diameterthe lower opening 45 of the receiving part 4, the sleeve-like insertpiece 5 cannot escape through the lower edge of the lower opening 45.Then, as shown in FIGS. 7 c and 7 d the sleeve-like insert piece 5 istilted so that it is finally seated in the seat portion 46 of thereceiving part 4, as shown in FIG. 7 d.

Thereafter, the bone anchoring element 1 is inserted, for example, fromthe top end 4 a of the receiving part 4 until the outer surface portion3 a of the head 3 engages the seat portion 52 of the sleeve-like insertpiece 5, as can be seen in FIGS. 7 e and 7 f. Then, the pressure member6 is inserted from the top end 4 a, as can be seen in FIG. 7 g, and apredefined force is applied from the top, as indicated by the arrow inFIG. 7 h. The pressure member 6 is arranged in an aligned position, inwhich the cylindrical recess 63 is aligned with the U-shaped recess 42of the receiving part 4 for receiving the rod 100. Dependent on thedegree of the interference fit connection, it may be necessary to use atool for pushing down the pressure member 6 into the receiving part 4.The predefined force from above may be generated manually or by a tool,for example, and may be constant and/or force-controlled orpath-controlled.

The bone anchoring device as a whole or in parts is made of abio-compatible material, such as a bio-compatible metal, for exampletitanium, stainless steel, of a bio-compatible alloy, such as nitinol,or of a bio-compatible plastic material, such as, for example,polyetheretherketone (PEEK).

FIGS. 8 a to 10 show a second embodiment of a bone anchoring device.Parts and portions which are the same or similar to those of the firstembodiment are designated with the same reference numerals, and thedescriptions thereof may not be repeated. The bone anchoring deviceaccording to the second embodiment differs from the bone anchoringdevice of the first embodiment by the construction of the outer surface65′ of the pressure member 6′ and of the corresponding inner surface ofthe coaxial bore 41′ of the receiving part 4′. All other parts areidentical or similar to those of the first embodiment.

As can be seen, especially in FIG. 8 b, the inner surface of the coaxialbore 41′ is structured, for example, is roughened or fluted or groovedor ridged. The outer surface 65′ of the pressure member 6′ may also bestructured, for example, may also be roughened or fluted or grooved orridged. The surface interaction of the two surfaces prevents orrestricts the pressure member 6′ from inadvertently moving backwardstowards the first end 4 a′. Therefore, a holding function of theinterference fit connection is further increased. It is also possiblethat only one of the surfaces is structured as described above.

FIGS. 11 a to 13 show a third embodiment of a bone anchoring device.Parts and portions which are the same or similar to those of the firstembodiment are designated with same reference numerals, and thedescriptions thereof may not be repeated. The bone anchoring deviceaccording to the third embodiment differs from the bone anchoring deviceof the first embodiment by the construction of the pressure member 6″and the corresponding portions of the receiving part 4″. All other partsare identical or similar to those of the first embodiment.

Referring to the outer surface 65″ of the pressure member 6″, which hasan upper portion 65 a″ and a lower portion 65 b″ with slightly differentouter diameters, an interference fit in this embodiment may only bepresent at the lower portion 65 b″ of the outer surface of the pressuremember 6″, which contacts the inner surface of the coaxial bore 41″ ofthe receiving part 4″. Therefore, in this embodiment, only the diameterof the lower portion 65 b″ may be slightly larger than an inner diameterof the corresponding portion of the coaxial bore 41″. The diameter ofthe upper portion 65 a″ may be the same or smaller than the diameter ofthe coaxial bore 41″. The upper portion 65 a″ may further include twoprojections 67″ at the free ends of the legs of the pressure member 6″,where the projections 67″ extend radially outwards and can latch into anannular groove 48″ provided in the coaxial bore 41″ of the receivingpart 4″ when the pressure member 6″ is inserted into the receiving part4″. Due to the larger outer diameter of the projections 67″ with respectto the inner diameter of the rest of the coaxial bore 41″, the legs ofthe pressure member 6″ may be compressed towards each other andelastically expand when the projections 67″ snap into the grooves 48″.

Pre-assembling of the bone anchoring device according to the second andthird embodiments corresponds or are similar to the pre-assemblingaccording to the first embodiment.

FIG. 14 shows a fourth embodiment of a bone anchoring device. Parts andportions which are the same or similar to those of the first embodimentare designated with same reference numerals, and the descriptionsthereof may not be repeated. The bone anchoring device according to thefourth embodiment differs from the bone anchoring device according tothe first embodiment that there is no interference fit connectionbetween the receiving part 4′″ and the pressure member 6′″, where anouter diameter of at least one portion of the pressure member 6′″ isequal to or smaller than an inner diameter of the corresponding portionsof the receiving part 4′″. Instead, a set screw 9′″ is provided which isscrewed into a through bore 49′″ located in one leg of the receivingpart 4′″ during assembly, for fixing the pressure member 6′″ relative tothe receiving part 4′″. The set screw 9′″ has an engagement portion 92′″for engagement with a tool and a flat bottom side 91′″ for cooperatingwith the outer surface 65′″ of the pressure member 6′″. All other partsare identical or similar to those of the first embodiment.

The first steps of pre-assembling the bone anchoring device according tothe fourth embodiment correspond or are similar to the pre-assemblingaccording to the first embodiment. A predefined force is applied on thepressure member 6′″ from above to define or determine a preload forceacting on the head 3′″. After that, the pressure member 6′″ isfrictionally fixed by screwing in the set screw 9′″. The set screw 9′″only acts radially, or perpendicular to an axis C″″, onto the outersurface 65′″ of the pressure member 6′″, and the pressure member 6″″ isthereby held in place. Therefore, the preload force acing on the head3″″ is maintained.

FIG. 15 shows a fifth embodiment of a bone anchoring device. Parts andportions which are the same or similar to those of the first embodimentare designated with same reference numerals, and the descriptionsthereof may not be repeated. The bone anchoring device according to thefifth embodiment differs from the bone anchoring device according to thefirst embodiment in that there no interference fit connection betweenthe receiving part 4″″ and the pressure member 6″″, where an outerdiameter of at least one portion of the pressure member 6″″ is equal toor smaller than an inner diameter of the corresponding portions of thereceiving part 4″″. A crimping blind hole 10″″ is provided, which islocated in one leg of the receiving part 4″″. All other parts areidentical or similar to those of the first embodiment.

The first steps of pre-assembling the bone anchoring device according tothe fifth embodiment correspond or are similar to the pre-assemblingaccording to the first embodiment. A predefined force is applied on thepressure member 6″″ from above to define or determine a preload forceacting on the head 3″″. After that, the pressure member 6″″ can befrictionally fixed by crimping, for example, by means of a crimpingtool. Here, a deformable portion 10 a″″ of the receiving part 4″″adjacent to the crimping blind hole 10″″ can be deformed, and thedeformed material radially exerts a pressure force onto the outersurface 65″″ of the pressure member 6″″, by which the pressure member6″″ is held in place. Therefore, the preload force acting on the head3″″ can be maintained.

Further modifications of the embodiments described are also conceivable.For example, for the bone anchoring element, various different kinds ofanchoring elements can be used and combined with the receiving parts.Such bone anchoring elements may be, for example, screws of differentlengths, screws with different diameters, cannulated screws, screws withdifferent thread forms, nails, hooks, etc. In some embodiments, the headand the shaft of the anchoring element may also be separate parts thatare connectable to each other.

Further modifications of the receiving part may include, for example, arecess for the rod that is inclined or open to the side, instead of aU-shaped recess which is perpendicular to a central axis of thereceiving part. Other kinds of locking devices, including outer nuts,outer caps, bayonet locking devices, or various other devices, may alsobe utilized. In embodiments of the invention, an inner surface portionof the pressure member that contacts the head may not necessarily bespherical-shaped, and can have any other shape suitable for exertingpressure onto the head of the bone anchoring element.

In some embodiments, it is also possible to use a two-part lockingdevice for separately fixing the rod and the head of the bone anchoringelement relative to the receiving part.

In some embodiments, it is also possible that the pressure member can beprevented from rotation by additional crimping.

It shall further be noted that portions or features of the variousdifferent embodiments described above can be combined with one another.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

What is claimed is:
 1. A polyaxial bone anchoring device comprising: abone anchoring element having a head and a shaft for anchoring to abone; a receiving part for coupling the bone anchoring element to a rod,the receiving part having a head receiving portion with an accommodationspace for accommodating the head, and a rod receiving portion having aninner wall defining a bore in communication with the accommodationspace, the bore having a bore axis; and a pressure member movable in thebore and comprising a first surface for engaging the head and a secondsurface for engaging a rod; wherein when the bone anchoring element andthe pressure member are in the receiving part, the pressure member ismovable to a first position where friction between the first surface andthe head generates a preload on the head to maintain the shaft at atemporary angular position relative to the receiving part, and to asecond position different from the first position where the head islocked relative to the receiving part; and wherein the pressure memberis configured to engage a first portion of the inner wall of thereceiving part that faces the bore axis without a positive lock, whereina holding force is generated at the engagement between the pressuremember and the first portion of the inner wall of the receiving part forholding the pressure member at the first position, and wherein thepressure member is movable out of the first position by applying anaxial force on the pressure member that is greater than the holdingforce.
 2. The poyaxial bone anchoring device of claim 1, wherein thepressure element is held at the first position by a radial force thatgenerates friction between the pressure member and the first portion ofthe inner wall of the receiving part.
 3. The polyaxial bone anchoringdevice of claim 1, wherein the pressure member is configured to form aninterference fit with the receiving part in the first position.
 4. Thebone anchoring device of claim 1, wherein at least a portion of asurface defining the bore is roughened, fluted, grooved or ridged. 5.The bone anchoring device of claim 1, wherein at least a portion of anouter surface of the pressure member is roughened, fluted, grooved orridged.
 6. The bone anchoring device of claim 1, wherein the pressuremember further comprises two projections extending radially outwards andconfigured to latch into annular grooves in the receiving part when thepressure member is in the receiving part.
 7. The bone anchoring deviceof claim 1, wherein the pressure member is substantially cylindrical. 8.The bone anchoring device of claim 1, wherein the first surface of thepressure member defines a recess at an end of the pressure member with aspherical-segment shape corresponding to a spherical-segment shapedsurface portion of the head of the bone anchoring element.
 9. The boneanchoring device of claim 1, further comprising a sleeve-like insertpiece configured to be positioned around a spherical-segment shapedportion of the head, wherein the insert piece is configured to pivot inthe accommodation space of the receiving part, and wherein when theinsert piece is seated in the receiving part and has a central axiscoaxial with the bore axis, a lower edge of the insert piece extends outof a lower opening of the receiving part.
 10. The polyaxial boneanchoring device of claim 1, wherein the receiving part comprises a setscrew, and wherein the pressure member is held in the first positionwhen the set screw extends into the bore and is in frictional contactwith an outer surface of the pressure member.
 11. The polyaxial boneanchoring device of claim 1, wherein the pressure member is held in thefirst position by crimping a portion of either the pressure member orthe receiving part.
 12. A method of manufacturing a polyaxial boneanchoring device comprising a bone anchoring element having a head and ashaft for anchoring to a bone, a receiving part for coupling the boneanchoring element to a rod, the receiving part having a head receivingportion with an accommodation space for accommodating the head, and arod receiving portion having an inner wall defining a bore incommunication with the accommodation space, the bore having a bore axis,and a pressure member comprising a first surface for engaging the headand a second surface for engaging a rod, wherein when the bone anchoringelement and the pressure member are in the receiving part, the pressuremember is movable to a first position where friction between the firstsurface and the head generates a preload on the head to maintain theshaft at a temporary angular position relative to the receiving part,and to a second position different from the first position where thehead is locked relative to the receiving part, the method comprising:inserting the head of the bone anchoring element in the receiving part;inserting the pressure member in the receiving part; applying an axialforce on the pressure member to move the pressure member to the firstposition to generate the preload on the head of the bone anchoringelement, wherein the pressure member engages a first portion of theinner wall of the receiving part that faces the bore axis without apositive lock, wherein a holding force is generated at the engagementbetween the pressure member and the first portion of the inner wall ofthe receiving part for holding the pressure member at the firstposition, and wherein the pressure member is movable out of the firstposition by applying an axial force on the pressure member that isgreater than the holding force.
 13. The method of claim 12, wherein theholding force is a radially acting force.
 14. The method of claim 13,wherein the radially acting force is generated by an interference fitbetween the pressure member and the receiving part.
 15. The method ofclaim 13, wherein the receiving part comprises a set screw, and whereinthe radially acting force is generated by screwing the set screw into athrough bore in the receiving part to exert pressure on the pressuremember.
 16. The method of claim 13, further comprising crimping one ofthe receiving part or the pressure member, wherein the radially actingforce is generated by a deformed portion formed by the crimping exertingpressure between the pressure member and the receiving part.
 17. Amethod for coupling a rod to a bone via a polyaxial bone anchoringdevice comprising a bone anchoring element having a head and a shaft foranchoring to a bone, a receiving part for coupling the bone anchoringelement to a rod, the receiving part having a head receiving portionwith an accommodation space for accommodating the head, and a rodreceiving portion having an inner wall defining a bore in communicationwith the accommodation space, the bore having a bore axis, and apressure member movable in the bore and comprising a first surface forengaging the head and a second surface for engaging a rod, and afixation element, the method comprising: inserting the bone anchoringelement into a bone when the head and the pressure member are in thereceiving part and the pressure member is at a first position wherefriction between the first surface and the head generates a preload ontothe head to maintain the shaft at a temporary angular position relativeto the receiving part; applying a force greater than the friction on thebone anchoring element or the receiving part to adjust the angularposition of the shaft relative to the receiving part, while the pressuremember engages a first portion of the inner wall of the receiving partthat faces the bore axis without a positive lock, wherein a holdingforce is generated at the engagement between the pressure member and thefirst portion of the inner wall of the receiving part for holding thepressure member at the first position; inserting a rod into the rodreceiving portion of the receiving part; advancing the fixation elementin the receiving part to advance the rod towards the head receivingportion, and to exert an axial force on the pressure member greater thanthe holding force to advance the pressure member out of the firstposition to a second position, to lock the head relative to thereceiving part and to lock a position of the rod relative to thereceiving part.
 18. The method of claim 17, further comprising:inserting the head of the bone anchoring element into the accommodationspace of the receiving part; inserting the pressure member into thereceiving part; and applying an axial force on the pressure membergreater than the holding force to move the pressure member into thefirst position.
 19. The method of claim 17, further comprising:inserting the head of the bone anchoring element into the accommodationspace of the receiving part; inserting the pressure member into thereceiving part; advancing the pressure member to the first position; andadvancing a set screw into the bore of the receiving part to engage thepressure member and to generate the holding force between the pressuremember and the receiving part.
 20. The method of claim 17, furthercomprising: inserting the head of the bone anchoring element into theaccommodation space of the receiving part; inserting the pressure memberinto the receiving part; advancing the pressure member to the firstposition; and crimping one of the receiving part or the pressure memberto engage the other one of the receiving part or the pressure member togenerate the holding force between the pressure member and the receivingpart.